JP4375534B2 - Fuel pressure detection device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel pressure detection of an internal combustion engine having a fuel pressure sensor for detecting a fuel pressure on a discharge side of a high pressure pump in a high pressure fuel supply system in which fuel discharged from a low pressure pump is pressurized by a high pressure pump and pumped to a fuel injection valve. It relates to the device.

  In a cylinder injection engine that directly injects fuel into a cylinder, in order to ensure combustibility, it is necessary to increase the injection pressure to promote atomization of the injected fuel. Therefore, in the cylinder injection engine, the fuel pumped up from the fuel tank by the electric low-pressure pump is pressurized to a high pressure by a mechanical high-pressure pump driven by the cam shaft of the engine and sent to the fuel injection valve. Yes. In such a high-pressure fuel supply system, the pressure of the fuel discharged from the high-pressure pump to the fuel injection valve is detected by a fuel pressure sensor, and the fuel injection amount (fuel injection time) of the fuel injection valve is corrected based on the detected fuel pressure. I have to. Therefore, when the detection accuracy of the fuel pressure sensor is poor, the correction accuracy of the fuel injection amount is deteriorated.

Therefore, as shown in Patent Document 1 (Japanese Patent Laid-Open No. 2000-249017), a technique for calibrating the detected fuel pressure of the fuel pressure sensor has been proposed. In this case, the output voltage of the fuel pressure sensor (detected fuel pressure) when the discharge pressure of the electric low-pressure pump reaches the maximum pressure (4 bar) and the discharge pressure of the mechanical high-pressure pump reach the maximum pressure (120 bar). A straight line connecting the output voltage (detected fuel pressure) of the fuel pressure sensor at this time is obtained as a calibration line, and the output voltage of the fuel pressure sensor is converted to the detected fuel pressure based on this calibration line.
JP 2000-249017 A (paragraph [0042], FIG. 3 etc.)

  In Patent Document 1, the output voltage (detected fuel pressure) of the fuel pressure sensor when the discharge pressure of the electric low-pressure pump reaches the maximum pressure (4 bar) and the discharge pressure of the mechanical high-pressure pump are the maximum pressure (120 bar). ), The straight line connecting the output voltage of the fuel pressure sensor (detected fuel pressure) is calculated as the calibration line. However, the maximum discharge pressure of the electric low-pressure pump is determined by the battery voltage and fuel temperature as the power source. As the fuel pressure sensor detection characteristics are corrected (calibrated) based on the maximum discharge pressure of the low-pressure pump, the fluctuation of the maximum discharge pressure of the low-pressure pump due to changes in battery voltage and fuel temperature. Detection error occurs, and the correction accuracy of the detected fuel pressure of the fuel pressure sensor is poor.

  The present invention has been made in view of such circumstances. Accordingly, an object of the present invention is to provide a fuel pressure detection device for an internal combustion engine that can improve the correction accuracy of the detected fuel pressure of the fuel pressure sensor.

In order to achieve the above object, the invention according to claim 1 is a system in which fuel is sent to a high pressure pump while adjusting a discharge pressure of a low pressure pump to a target discharge pressure, and a detected fuel pressure of a fuel pressure sensor is a predetermined value or less. When there is a predetermined learning execution condition that the low fuel pressure region of the fuel is low and the condition is satisfied , the detection error of the fuel pressure sensor based on the deviation between the target discharge pressure of the low pressure pump and the detected fuel pressure of the fuel pressure sensor by the learning means And the detected fuel pressure of the fuel pressure sensor is corrected by the detected fuel pressure correcting means based on the learned value from the low fuel pressure region after the learning is completed. In this case, the reference value (target discharge pressure of the low-pressure pump) used for learning the detection error of the fuel pressure sensor does not change even when the battery voltage or the fuel temperature changes, so the fuel pressure sensor is based on the target discharge pressure of the low-pressure pump. If this detection error is learned, the detection error of the fuel pressure sensor can be learned with high accuracy without being affected by changes in the battery voltage and the fuel temperature, and the correction accuracy of the detected fuel pressure of the fuel pressure sensor can be improved.

  In general, the detection characteristics of the fuel pressure sensor that detects the fuel pressure on the discharge side of the high-pressure pump are designed so that the detection accuracy is high in the high fuel pressure region normally used during operation of the internal combustion engine. There is a tendency for accuracy to deteriorate.

Such a fuel pressure sensor detecting characteristics in consideration of, in the invention according to claim 1, the detection fuel pressure of the fuel pressure sensor is adapted to learn the detection error of the fuel pressure sensor at low fuel pressure region below the predetermined value, the fuel pressure sensor In the low fuel pressure region (in other words, the region in which the detection error of the fuel pressure sensor is easy to learn) , the detection error of the fuel pressure sensor can be learned with high accuracy.

Further, as in claim 2 , when the deviation δ1 (= target discharge pressure−actual fuel pressure) between the target discharge pressure of the low pressure pump and the fuel pressure (actual fuel pressure) on the discharge side of the high pressure pump can be estimated, the fuel pressure It is preferable to learn the detection error of the sensor. In this way, by detecting the deviation δ2 (= target discharge pressure−detected fuel pressure) between the target discharge pressure of the low pressure pump and the detected fuel pressure of the fuel pressure sensor, the detection error of the fuel pressure sensor (= detected fuel pressure−actual fuel pressure = [delta] 1- [delta] 2) can be learned with high accuracy.

For example, as according to claim 3, elevated both deviation δ1 to 0 (the actual fuel pressure = target discharge from the low pressure pump is started to the target discharge pressure of the fuel pressure on the discharge side (actual fuel pressure) is low pressure pump of the high pressure pump It is preferable to learn the detection error of the fuel pressure sensor when it can be estimated that the pressure has reached. In this way, the detection error of the fuel pressure sensor can be learned with high accuracy by a simple process.

More specifically, when a predetermined time required for the fuel pressure (actual fuel pressure) on the discharge side of the high-pressure pump to rise to the target discharge pressure of the low-pressure pump has elapsed since the low-pressure pump was started, as in claim 4. Furthermore, it is preferable to learn the detection error of the fuel pressure sensor. Thus, if the learning timing is determined from the elapsed time after the low-pressure pump is started, the learning timing can be easily determined.

Further, as described in claim 5 , the detection error of the fuel pressure sensor may be learned for each specific operating parameter region that affects the fuel pressure. In this way, even when the detection error of the fuel pressure sensor changes due to a change in a specific operation parameter, the detection error of the fuel pressure sensor can be learned and corrected with high accuracy.

For example, since the detection error of the fuel pressure sensor tends to change depending on the fuel temperature, in a system including temperature detection means for detecting the fuel temperature or any temperature correlated therewith, as in claim 6 , You may make it learn the detection error of the said fuel pressure sensor for every area | region of the temperature detected by the temperature detection means. In this way, the detection error of the fuel pressure sensor can be learned and corrected with high accuracy without being affected by the fuel temperature.

Also, short stopping time of the internal combustion engine, when the low-pressure pump is activated in the absence Kira missing residual fuel pressure on the discharge side of the high-pressure pump, it is preferable to avoid learning the sensing error of the fuel pressure sensor. When the low-pressure pump is started in a state where the residual fuel pressure on the discharge side of the high-pressure pump is not completely removed, the discharge pressure of the low-pressure pump at the beginning of the start-up is unknown, and the subsequent increase in the discharge pressure of the low-pressure pump cannot be estimated. The timing at which the fuel pressure (actual fuel pressure) on the discharge side of the high-pressure pump rises to the target discharge pressure of the low-pressure pump cannot be accurately estimated. In such a case, if the detection error of the fuel pressure sensor is not learned, it is possible to prevent erroneous learning and learning accuracy deterioration due to the residual fuel pressure on the discharge side of the high-pressure pump.

As the low pressure pump discharge pressure adjusting means for adjusting the discharge pressure of the low pressure pump to the target discharge pressure, in a system using a fuel pressure regulator, as the target discharge pressure of the low pressure pump, it may be to use a set pressure of the pressure regulator.

In a system for feedback controlling the discharge pressure of the low pressure pump to the target value as the target discharge pressure of the low pressure pump, it may be to use a target value of feedback control. Regardless of whether the set pressure of the fuel pressure regulator or the target value of feedback control is used, the detection error of the fuel pressure sensor can be accurately learned without being affected by changes in the battery voltage or fuel temperature.

In the present invention, the detected fuel pressure of the fuel pressure sensor may be corrected based on the learning value of the learning means in all fuel pressure regions, but in general, the detection characteristic of the fuel pressure sensor is normally used during operation of the internal combustion engine. since it is designed as detection accuracy in the high fuel pressure region increases, learning detected fuel pressure fuel pressure sensor is only learning means at a predetermined value below the low fuel pressure region (low fuel pressure region detection error of the fuel pressure sensor can not be ignored) The detected fuel pressure of the fuel pressure sensor may be corrected based on the value. In this way, in the high fuel pressure region that is normally used during operation of the internal combustion engine (the region where the detection accuracy of the fuel pressure sensor is high), it is not necessary to perform inherently unnecessary learning correction, reducing the computational load on the in-vehicle computer. can do.

In this case, it is preferable so as to limit the upper limit of detection fuel pressure after compensation with low fuel pressure region (Correction There region) and the boundary between the high fuel pressure region (uncorrected area) the fuel pressure (a predetermined value). By doing so, it is possible to prevent the detected fuel pressure after correction from becoming discontinuous at the boundary between the low fuel pressure region (region with correction) and the high fuel pressure region (region without correction).

Furthermore, may the fuel injection amount of the fuel injection valve so as to correct the injection amount correction means using the detection fuel pressure after compensation. In this way, the fuel injection amount can be corrected with high accuracy even in the low fuel pressure region at the start when the detection accuracy of the fuel pressure sensor is reduced, and the startability can be improved.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the configuration of a high-pressure fuel supply system for a direct injection engine (internal combustion engine) will be described with reference to FIG. An electric low-pressure pump 12 that pumps up the fuel is disposed in the fuel tank 11 that stores the fuel. The low-pressure pump 12 is driven by an electric motor (not shown) that uses a battery (not shown) as a power source. The fuel discharged from the low-pressure pump 12 is supplied to a mechanical high-pressure pump 14 through a low-pressure side fuel pipe 13. A fuel pressure regulator 15 (low pressure pump discharge pressure adjusting means) is provided in the middle of the low pressure side fuel pipe 13, and the discharge pressure of the low pressure pump 12 (fuel supply pressure to the high pressure pump 14) is set to the target discharge pressure by the fuel pressure regulator 15. The surplus of the fuel that is adjusted to (for example, 0.4 MPa) and exceeds the target discharge pressure is returned into the fuel tank 11 by the fuel return pipe 16.

  As shown in FIG. 2, the high-pressure pump 14 is a plunger pump that sucks / discharges fuel by reciprocating a plunger 19 in a cylindrical pump chamber 18, and the plunger 19 is fitted to a cam shaft 20 of the engine. It is driven by the rotational movement of the cam 21. Thereby, as shown in FIG. 3, the lift amount of the plunger 19 changes periodically according to the crank angle.

  As shown in FIG. 2, a flow control valve 22 is provided on the suction port 23 side of the pump chamber 18. This flow control valve 22 is a normally-open electromagnetic valve, and a valve body 26 that opens and closes the suction port 23, a spring 27 that urges the valve body 26 in the valve opening direction, and a valve body 26 in the valve closing direction. It is composed of a norenoid 28 that is electromagnetically driven. When the drive current is not supplied to the solenoid 28, the valve element 26 is opened by the biasing force of the spring 27, and the suction port 23 is opened. On the other hand, when a drive current is applied to the solenoid 28, the valve body 26 is closed against the biasing force of the spring 27 by the electromagnetic driving force of the solenoid 28 and the suction port 23 is closed.

  In the suction stroke of the high-pressure pump 14 (stroke in which the plunger 19 moves from the top dead center to the bottom dead center), the flow control valve 22 is opened, fuel is sucked into the pump chamber 18, and the discharge stroke (plunger 19 is lowered). By controlling the valve closing start timing of the flow rate control valve 22 in the process of moving from the dead center to the top dead center, the fuel discharge amount is adjusted, and the discharge fuel pressure of the high-pressure pump 14 (hereinafter referred to as “high-pressure side fuel pressure”). ) To control.

  For example, when increasing the high-pressure side fuel pressure, the closing timing of the flow rate control valve 22 is advanced from, for example, the timing of the solid line to the dotted line in FIG. 3 to increase the valve closing period (effective stroke) until the end of the discharge stroke. When the discharge amount is increased and, conversely, when the high-pressure side fuel pressure is decreased, the closing timing of the flow control valve 22 is delayed from the dotted line to the solid line, for example, in FIG. Stroke) is shortened to reduce fuel discharge. At this time, during the period in which the flow rate control valve 22 is open in the discharge stroke, the fuel flows backward to the low pressure side and a large pulsation is generated by the pumping action, so the pulsation damper 34 described later absorbs the pulsation. It is like that.

  On the other hand, a check valve 25 for preventing the backflow of discharged fuel is provided on the discharge port 24 side of the high-pressure pump 14. As shown in FIG. 1, the fuel discharged from the high-pressure pump 14 is pumped to the delivery pipe 30 through the high-pressure side fuel pipe 29, and high-pressure fuel is distributed from the delivery pipe 30 to the fuel injection valve 31 of each cylinder. . The delivery pipe 30 is provided with a fuel pressure sensor 32 that detects the high-pressure side fuel pressure. The fuel pressure sensor 32 incorporates a fuel temperature sensor 33 (temperature detection means) that detects the fuel temperature. Needless to say, the fuel temperature sensor 33 may be provided at a position different from the fuel pressure sensor 32.

  A pulsation damper 34 for reducing the pulsation of fuel pressure on the suction port 23 side of the high-pressure pump 14 (hereinafter referred to as “low-pressure side fuel pressure”) is connected to the connection portion between the suction port 23 of the high-pressure pump 14 and the low-pressure side fuel pipe 13. Is connected. The pulsation damper 34 has a built-in diaphragm (not shown) that absorbs the pulsation of the low-pressure side fuel pressure and stabilizes the low-pressure side fuel pressure.

  As shown in FIG. 10, the fuel pressure on the discharge side of the high-pressure pump 14 is maintained at a high pressure (for example, around 9 MPa) during engine operation, but the fuel pressure on the discharge side of the high-pressure pump 14 remains high after the engine is stopped. It gradually escapes from the internal gap and drops to near atmospheric pressure in a few hours. Therefore, when starting the engine thereafter, the fuel pressure on the discharge side of the high-pressure pump 14 is increased from near atmospheric pressure to high pressure (for example, near 9 MPa), but until the engine speed rises to some extent at the time of starting, Since the fuel pressure cannot be quickly increased by the high-pressure pump 14, the discharge pressure of the low-pressure pump 12 is directly transmitted to the delivery pipe 30 through the high-pressure pump 14 while the flow rate control valve 22 is held fully open. Therefore, fuel injection control is performed with the discharge pressure (for example, 0.4 MPa) of the low-pressure pump 12 until the engine speed increases to some extent at the time of starting. When the engine speed rises to some extent and the discharge capacity of the high pressure pump 14 exceeds the required injection amount, the control of closing / opening the flow rate control valve 22 is started, and the fuel pressure feed by the high pressure pump 14 is started. To start.

  Output signals (detected fuel pressure) of the fuel pressure sensor 32 and the fuel temperature sensor 33 are input to the ECU 36. The ECU 36 is mainly composed of a microcomputer, and executes the detection error learning correction routine shown in FIG. 7 stored in a built-in ROM (storage medium), whereby the low pressure pump 12 is set when a predetermined learning execution condition is satisfied. The detection error of the fuel pressure sensor 32 is learned on the basis of the deviation between the target discharge pressure and the detected fuel pressure of the fuel pressure sensor 32, and the detected fuel pressure of the fuel pressure sensor 32 is corrected based on the learned value.

Here, the learning correction method of the detected fuel pressure of the fuel pressure sensor 32 will be described.
In general, as shown in FIG. 4, the detection characteristic of the fuel pressure sensor 32 is not linear (straight line) but a quadratic curve, and the detection accuracy is high in a high fuel pressure region (for example, around 9 MPa) normally used during engine operation. Designed to be high.

  Further, as shown in FIG. 5, the allowable error of the fuel pressure sensor 32 is about ± 2% to ± 4% with respect to the maximum detected value, and the allowable error is up to about ± 4% in the extremely low temperature range where the environmental conditions are severe. Becomes larger. For example, if the maximum detected value of the fuel pressure sensor 32 is 20 MPa, an allowable error of 20 MPa × 0.02 = 0.4 MPa exists even in a normal temperature range (25 ° C. atmosphere) where the allowable error is minimum (± 2%). . When starting fuel injection control similar to the prior art is performed using this fuel pressure sensor 32, the starting fuel is detected at a detected fuel pressure that includes an error of ± 0.4 MPa with respect to the actual fuel pressure of about 0.4 MPa even in a normal temperature range. The injection amount is corrected, and the correction accuracy is extremely deteriorated.

  In the present embodiment, a fuel pressure correction coefficient map having the characteristics shown in FIG. 6 is searched to obtain a fuel pressure correction coefficient K corresponding to the detected fuel pressure at that time, and this fuel pressure correction coefficient K is multiplied by the base injection amount to obtain a final result. However, when the fuel pressure correction coefficient K is obtained with the detected fuel pressure (0.8 MPa) including an error of +0.4 MPa with respect to the actual fuel pressure of 0.4 MPa as in the prior art. Although the fuel pressure correction coefficient K is actually 8.0, the fuel pressure correction coefficient K becomes 4.0, and only a fuel amount that is ½ of the required fuel injection amount can be injected. There is a problem that the sex gets worse. Such a problem becomes a larger problem in a low temperature range where the tolerance of the fuel pressure sensor 32 becomes large.

  As described above, when the engine is started, it is not possible to quickly increase the fuel pressure by the high pressure pump 14, so that the delivery pressure of the discharge pressure of the low pressure pump 12 passes through the high pressure pump 14 with the flow rate control valve 22 held fully open. Is transmitted to the side. In consideration of the characteristics of the fuel pressure control at the time of starting, in this embodiment, the fuel pressure (actual fuel pressure) on the discharge side of the high pressure pump 14 from the start of the low pressure pump 12 (turning on the ignition switch) is The time when the time required to increase to the target discharge pressure (set pressure of the fuel pressure regulator 15) has elapsed is set as the learning timing, and at this learning timing, the detected fuel pressure of the fuel pressure sensor 32 is read into the ECU 36 and the target of the low-pressure pump 12 is read. A deviation between the discharge pressure and the detected fuel pressure of the fuel pressure sensor 32 is calculated, and this deviation is stored as a detected error learning value of the fuel pressure sensor 32 in a rewritable nonvolatile memory (not shown) such as a backup RAM of the ECU 36. Thereafter, the fuel pressure correction coefficient K is calculated using the value obtained by adding the detection error learning value to the detected fuel pressure of the fuel pressure sensor 32 as the final detected fuel pressure, and this fuel pressure correction coefficient K is multiplied by the base injection amount to obtain the final value. To determine the optimal fuel injection amount.

  In this case, the detected fuel pressure of the fuel pressure sensor 32 may be corrected using the detection error learning value of the fuel pressure sensor 32 in all the fuel pressure regions, but in general, the detection characteristic of the fuel pressure sensor 32 is normal during engine operation. In this embodiment, the detection accuracy of the fuel pressure sensor 32 is detected only in a low fuel pressure region (for example, a region of 2 MPa or less) where the detection error of the fuel pressure sensor 32 cannot be ignored. The error is learned and corrected.

  By the way, when the low pressure pump 12 is started in a state where the engine stop time is short and the residual fuel pressure on the discharge side of the high pressure pump 14 is not exhausted, the discharge pressure of the low pressure pump 12 at the initial start is unknown, and the subsequent low pressure pump Therefore, the timing at which the fuel pressure (actual fuel pressure) on the discharge side of the high-pressure pump 14 rises to the target discharge pressure of the low-pressure pump 12 cannot be accurately estimated. Therefore, in the present embodiment, the ECU 36 measures the engine stop time after the ignition switch (hereinafter abbreviated as “IG switch”) is turned off, and the high-pressure pump is operated when the engine stop time is less than a predetermined time (for example, 2 hours or less). When the low-pressure pump 12 is activated in a state where the residual fuel pressure on the discharge side of 14 is not completely removed, a fuel pressure sensor is used to prevent erroneous learning and a decrease in learning accuracy due to the residual fuel pressure on the discharge side of the high-pressure pump 14. 32 detection errors are not learned.

  In addition, since the detection error of the fuel pressure sensor 32 tends to change depending on the fuel temperature, in this embodiment, the detection error of the fuel pressure sensor 32 is learned for each region of the fuel temperature detected by the fuel temperature sensor 33. .

  The learning correction of the detected fuel pressure of the fuel pressure sensor 32 described above is executed by the ECU 36 according to the detection error learning correction routine of FIG. This routine is repeatedly executed at a predetermined cycle after the IG switch is turned on, and functions as learning means in the claims. When this routine is started, first, in steps 101 to 103, whether or not the learning execution condition is satisfied is determined by whether or not all three conditions are satisfied as follows. First, in step 101, it is determined whether or not the detected fuel pressure HP of the fuel pressure sensor 32 is lower than a predetermined value (for example, 2 MPa), which is a low fuel pressure region where the detection error of the fuel pressure sensor 32 cannot be ignored.

  If it is determined in step 101 that the detected fuel pressure HP of the fuel pressure sensor 32 is lower than a predetermined value (for example, 2 MPa), it is determined that the detection error of the fuel pressure sensor 32 cannot be ignored, and the process proceeds to step 102. It is determined whether the residual fuel pressure on the discharge side of the high-pressure pump 14 is completely released during the engine stop by determining whether the engine stop time CIGOFF before the start is longer than a predetermined time (for example, 2 hours). To do.

  If it is determined in step 102 that the engine stop time CIGOFF before the start is longer than a predetermined time (for example, 2 hours), the process proceeds to step 103 and the elapsed time CIGON after the IG switch is turned on (after the low pressure pump 12 is started) Whether the fuel pressure (actual fuel pressure) on the discharge side of the high-pressure pump 14 is equal to a predetermined time CHPNT required for the pressure to rise to the target discharge pressure (set pressure of the fuel pressure regulator 15) of the low-pressure pump 12 or not. Thus, it is determined whether or not the fuel pressure (actual fuel pressure) on the discharge side of the high-pressure pump 14 matches the target discharge pressure (set pressure of the fuel pressure regulator 15) of the low-pressure pump 12 (whether or not it is the learning timing). Here, the predetermined time CHPNT may be set in advance to a certain time based on experimental data or design data, but the discharge pressure of the low-pressure pump 12 depends on the battery voltage or the fuel temperature as the power source of the low-pressure pump 12. The predetermined time CHPNT may be changed according to the battery voltage or the fuel temperature in consideration of a slight change in the rising behavior of the battery.

  The learning execution condition is satisfied only when all of the three steps 101 to 103 described above are determined as “Yes”. However, if “No” is determined in any of the three steps 101 to 103, the learning execution is performed. The condition is not satisfied.

  If it is determined “No” in the first step 101, that is, if the detected fuel pressure HP of the fuel pressure sensor 32 is determined to be a predetermined value (for example, 2 MPa) or more, the detection error of the fuel pressure sensor 32 can be ignored (detection). It is determined that learning correction of the fuel pressure HP is unnecessary), and the process proceeds to step 111, where the detected fuel pressure HP of the fuel pressure sensor 32 is stored as the final detected fuel pressure CHP as it is.

  When it is determined as “No” in the second step 102, that is, when the engine stop time CIGOFF before the start is shorter than a predetermined time (for example, 2 hours), the remaining on the discharge side of the high-pressure pump 14 during the engine stop. It is determined that the fuel pressure is not completely removed, the processing of steps 106 to 108 is executed, and the detection error of the fuel pressure sensor 32 is not learned, and the fuel pressure sensor 32 using the previous detection error learning value DHP. Only the correction of the detected fuel pressure HP is performed. Specifically, after the fuel temperature detected by the fuel temperature sensor 33 is read in step 106, the process proceeds to step 107, and a detection error learning value map stored in a rewritable nonvolatile memory of the ECU 36 (see FIG. 8). ) And a detection error learning value DHP corresponding to the current fuel temperature is read. Thereafter, the process proceeds to step 108, and the detected fuel pressure CHP corrected by the detected error learned value DHP is obtained by adding the detected error learned value DHP to the detected fuel pressure HP of the fuel pressure sensor 32.

  On the other hand, when it is determined as “No” in the third step 103, that is, the elapsed time CIGON after the IG switch is turned on (the elapsed time after the start of the low-pressure pump 12) does not coincide with the predetermined time CHPNT. Determines that the fuel pressure (actual fuel pressure) on the discharge side of the high-pressure pump 14 does not coincide with the target discharge pressure of the low-pressure pump 12 (not the learning timing), and executes the processing of steps 106 to 108. Thus, only the correction of the detected fuel pressure HP of the fuel pressure sensor 32 is performed using the previous detected error learning value DHP without learning the detection error of the fuel pressure sensor 32.

  On the other hand, if it is determined as “Yes” in the three steps 101 to 103, it is determined as the learning timing, and the process proceeds to step 104 where the target discharge pressure TFP of the low pressure pump 12 (the set pressure of the fuel pressure regulator 15) is determined. ) And the detected fuel pressure HP of the fuel pressure sensor 32 is calculated as a detected error learning value. Thereafter, the process proceeds to step 105, and the detection error learning value DHP corresponding to the current fuel temperature in the detection error learning value map (see FIG. 8) stored in the rewritable nonvolatile memory of the ECU 36 is set to the above step 104. The latest detection error learning value DHP calculated in step (1) is rewritten. Thereafter, the process proceeds to step 108, and the detected fuel pressure CHP corrected by the detected error learned value DHP is obtained by adding the detected error learned value DHP corresponding to the current fuel temperature to the detected fuel pressure HP of the fuel pressure sensor 32.

  Thereafter, the process proceeds to step 109, and whether or not the corrected detected fuel pressure CHP is lower than the fuel pressure at the boundary between the low fuel pressure region (corrected region) and the high fuel pressure region (non-corrected region) (2 MPa in this embodiment). If the corrected detected fuel pressure CHP is lower than the boundary fuel pressure (2 MPa), the corrected detected fuel pressure CHP is used as it is as the final detected fuel pressure CHP, but if the corrected detected fuel pressure CHP is the boundary If the fuel pressure exceeds 2 MPa, the process proceeds to step 110, where the final detected fuel pressure CHP is rewritten to the boundary fuel pressure (2 MPa). Thereby, the guard process which restrict | limits the upper limit of the detection fuel pressure CHP after correction | amendment by the fuel pressure (2 Mpa) of a boundary is performed. The processing in steps 108 to 110 described above plays a role as detected fuel pressure correcting means in the claims.

  Thereafter, the process proceeds to step 112, the fuel pressure correction coefficient map of FIG. 6 is searched to obtain the fuel pressure correction coefficient K corresponding to the final detected fuel pressure CHP, and then the process proceeds to step 113, where the fuel pressure correction coefficient K is used as a base. The final fuel injection amount FINJ is obtained by multiplying the injection amount INJ. Thereby, even in the low fuel pressure region where the detection accuracy of the fuel pressure sensor 32 is deteriorated, the accuracy of the final fuel injection amount FINJ is ensured, and accurate fuel injection control is possible. The processing of these steps 112 and 113 serves as an injection amount correction means in the claims.

  A control example using the detection error learning correction routine of FIG. 7 described above will be described with reference to time charts of FIGS.

  FIG. 9 illustrates the behavior of the high-pressure side fuel pressure (fuel pressure on the discharge side of the high-pressure pump 14) after the engine is stopped, and the behavior of the high-pressure side fuel pressure, the detected fuel pressure HP, and the corrected detected fuel pressure CHP when the engine is subsequently started. It is a time chart. When the IG switch is turned off during engine operation, a timer for measuring the engine stop time CIGOFF starts timing at the time t1. While the engine is stopped, the high-pressure side fuel pressure gradually escapes from the gap inside the high-pressure pump 14, and after about 2 hours, the high-pressure side fuel pressure is completely removed (a state where the pressure is reduced to near atmospheric pressure). In the present embodiment, one of the learning execution conditions is that the engine stop time CIGOFF is 2 hours or more.

  Thereafter, when the IG switch is turned on, at the time t2, the low pressure pump 12 is activated, and a timer for measuring the elapsed time CIGON (the elapsed time after the activation of the low pressure pump 12) after the IG switch is turned on starts the timing operation. Start. In the example of FIG. 9, the engine stop time CIGOFF before the start is 2 hours or longer, so that one condition of the learning execution condition is satisfied. However, after the low-pressure pump 12 is started, the high-pressure side fuel pressure is changed from near atmospheric pressure to the low-pressure pump 12. It takes a predetermined time CHPNT to increase to the target discharge pressure TFP (the set pressure of the fuel pressure regulator 15). Accordingly, until the elapsed time CIGON after the IG switch is turned on reaches the predetermined time CHPNT, the learning execution condition is not satisfied, and the fuel pressure is detected by using the previous detection error learning value DHP without learning the detection error of the fuel pressure sensor 32. Only the detection fuel pressure HP of the sensor 32 is corrected.

  Thereafter, at the time t3 when the elapsed time CIGON after turning on the IG switch reaches the predetermined time CHPNT, it is determined that the learning execution condition is satisfied and the high-pressure side fuel pressure matches the target discharge pressure TFP of the low-pressure pump 12, A deviation DHP (= TFP−HP) between the target discharge pressure TFP of the low-pressure pump 12 and the detected fuel pressure HP of the fuel pressure sensor 32 at the time point t3 is calculated as a detected error learning value, and detected error learning is performed on the detected fuel pressure HP of the fuel pressure sensor 32. The corrected detected fuel pressure CHP is obtained by adding the value DHP.

  When the elapsed time CIGON after the IG switch is turned on exceeds the predetermined time CHPNT, the learning execution condition is again not satisfied, and the detection error learning value DHP calculated at time t3 is not learned without learning the detection error of the fuel pressure sensor 32. Only the detected fuel pressure HP of the fuel pressure sensor 32 is corrected. This correction process is repeatedly executed at a predetermined cycle until the detected fuel pressure HP of the fuel pressure sensor 32 exceeds 2 MPa, which is the upper limit fuel pressure in the correction region.

  When the detected fuel pressure HP of the fuel pressure sensor 32 approaches 2 MPa, the corrected detected fuel pressure CHP may exceed 2 MPa (t4 to t5), and thus a guard process for limiting the upper limit of the corrected detected fuel pressure CHP to 2 MPa is performed. .

  Thereafter, at time t5 when the detected fuel pressure HP of the fuel pressure sensor 32 reaches 2 MPa, which is the upper limit fuel pressure in the correction region, it is determined that the detection error of the fuel pressure sensor 32 can be ignored (the learning correction of the detected fuel pressure HP is unnecessary). Then, the correction of the detected fuel pressure HP by the detected error learning value DHP is finished, and the detected fuel pressure HP of the fuel pressure sensor 32 is used as it is as the final detected fuel pressure CHP. In this case, before the time t5 when the detected fuel pressure HP is corrected by the detected error learning value DHP, the upper limit of the corrected detected fuel pressure CHP is guarded at 2 MPa, so the time t5 when the detected fuel pressure HP of the fuel pressure sensor 32 reaches 2 MPa. Therefore, even if the detected fuel pressure HP of the fuel pressure sensor 32 is used as it is as the final detected fuel pressure CHP, the final detected fuel pressure CHP does not become discontinuous before and after that.

  FIGS. 10A and 10B are time charts illustrating the behavior of the high-pressure side fuel pressure, the engine speed, and the battery voltage when starting at temperatures of −8 ° C. and −25 ° C., respectively. The starter is started at point a and cranking of the engine is started. However, since the engine speed is low at the time of cranking, a rapid increase in fuel pressure by the high pressure pump 14 cannot be expected (starting more than the discharge capacity of the high pressure pump 14). (This is because the required injection amount is required). Therefore, at the time of start-up, until the engine speed increases to some extent, the discharge pressure of the low-pressure pump 12 is directly transmitted to the delivery pipe 30 side through the high-pressure pump 14 while the flow rate control valve 22 is kept fully open. Therefore, fuel injection control is performed with the discharge pressure (0.4 MPa) of the low-pressure pump 12 until the engine speed increases to some extent at the start.

  Then, when the engine speed rises to some extent and the discharge capacity of the high-pressure pump 14 exceeds the required injection amount (point b in FIG. 10), the control for closing / opening the flow control valve 22 is started. Then, fuel pumping by the high-pressure pump 14 is started. As a result, the fuel pressure rises rapidly from the point where the high-pressure side fuel pressure exceeds about 1 MPa to the target fuel pressure (9 MPa in FIG. 10). Since the detection error of the fuel pressure sensor 32 cannot be ignored until the high-pressure side fuel pressure exceeds about 2 MPa, learning correction is necessary.

  The time required for the high-pressure side fuel pressure to exceed the low fuel pressure region required for the learning correction of the detection error of the fuel pressure sensor 32 becomes longer as the temperature decreases. Therefore, the importance of learning correction of the detection error of the fuel pressure sensor 32 increases as the temperature decreases.

  According to the present embodiment described above, the learning timing is the time when the predetermined time required for the high-pressure side fuel pressure to rise to the target discharge pressure of the low-pressure pump 12 has elapsed since the start of the low-pressure pump 12 (IG switch on operation). The deviation between the target discharge pressure of the low-pressure pump 12 and the detected fuel pressure of the fuel pressure sensor 32 is calculated as a detection error learning value at this learning timing, and the detected fuel pressure of the fuel pressure sensor 32 is corrected with the detected error learning value. ing. In this case, the reference value (the target discharge pressure of the low-pressure pump 12) used for learning the detection error of the fuel pressure sensor 32 does not change even when the battery voltage or the fuel temperature changes, so the reference discharge pressure of the low-pressure pump 12 is used as a reference. If the detection error of the fuel pressure sensor 32 is learned, the detection error of the fuel pressure sensor 32 can be learned with high accuracy without being affected by changes in the battery voltage and the fuel temperature, and the correction accuracy of the detected fuel pressure of the fuel pressure sensor 32 can be increased. Can be improved.

  Moreover, in this embodiment, the detection error of the fuel pressure sensor 32 is learned for each region of the fuel temperature detected by the fuel temperature sensor 33 in consideration of the characteristic that the detection error of the fuel pressure sensor 32 changes depending on the fuel temperature. Therefore, there is an advantage that learning accuracy can be improved. In this case, in a system that does not include the fuel temperature sensor 33, any temperature correlated with the fuel temperature (for example, cooling water temperature, engine oil temperature, etc.) may be used as fuel temperature substitute information.

  In the present invention, in addition to the fuel temperature, the detection error of the fuel pressure sensor 32 may be learned for each region of a specific operating parameter (for example, battery voltage) that affects the fuel pressure. You may make it learn the detection error of the fuel pressure sensor 32 for every area | region (for example, fuel temperature and battery voltage). Of course, in the present invention, a learning value common to all regions may be obtained without performing learning for each region.

  Further, in this embodiment, when the low-pressure pump 12 is started in a state where the engine stop time is short and the residual fuel pressure on the discharge side of the high-pressure pump 14 is not exhausted, the detection error of the fuel pressure sensor 32 is not learned. There is an advantage that it is possible to prevent erroneous learning and lowering of learning accuracy due to the residual fuel pressure on the discharge side of the high-pressure pump 14.

  In general, the detection characteristic of the fuel pressure sensor 32 is designed so that the detection accuracy is high in a high fuel pressure region that is normally used during engine operation. Therefore, in this embodiment, the detection error of the fuel pressure sensor 32 cannot be ignored. The detected fuel pressure of the fuel pressure sensor 32 is corrected based on the detected error learning value only in the low fuel pressure region. Thereby, in the high fuel pressure region (region where the detection accuracy of the fuel pressure sensor 32 is normally used) normally used during engine operation, it is not necessary to perform essentially unnecessary learning correction, and the calculation load of the ECU 36 can be reduced. There is.

  However, in the case of a detection characteristic system in which the same detection error occurs in the high fuel pressure region as in the low fuel pressure region, the detected fuel pressure of the fuel pressure sensor 32 may be corrected based on the detection error learning value in all the fuel pressure regions. good.

  Further, in the present embodiment, a guard process is performed to limit the upper limit of the detected fuel pressure after correction by the fuel pressure (2 MPa) at the boundary between the low fuel pressure region (region with correction) and the high fuel pressure region (region without correction). Therefore, there is an advantage that the corrected detected fuel pressure can be prevented from becoming discontinuous at the boundary (2 MPa) between the low fuel pressure region (region with correction) and the high fuel pressure region (region without correction).

  In this embodiment, the set pressure of the fuel pressure regulator 15 is used as the target discharge pressure of the low pressure pump 12, but in a system in which the fuel pressure regulator 15 is omitted and the discharge pressure of the low pressure pump 12 is feedback controlled to the target value, A target value for feedback control may be used as the target discharge pressure of the pump 12.

  In this embodiment, whether or not the fuel pressure on the discharge side of the high-pressure pump 14 (high-pressure side fuel pressure) has reached the target discharge pressure of the low-pressure pump 12 at the start-up (whether or not it is the learning timing) is determined. The determination is made based on the elapsed time CIGON (the elapsed time after the start of the low pressure pump 12) after being turned on. For example, during the fully open period of the flow control valve 22 after the IG switch is turned on (the low pressure pump 12 is on the high pressure side). During the period in which the fuel pressure is not increased), the rising curve of the detected fuel pressure of the fuel pressure sensor 32 is monitored, and when the detected fuel pressure of the fuel pressure sensor 32 almost ends and the detected fuel pressure becomes substantially constant, the discharge of the high pressure pump 14 It may be estimated that the side fuel pressure (high pressure side fuel pressure) has reached the target discharge pressure of the low pressure pump 12.

  Further, in the present embodiment, the number of times of detection error calculation per learning (learning frequency) is set to one time, but the fuel pressure on the discharge side of the high-pressure pump 14 (high-pressure side fuel pressure) is the target discharge of the low-pressure pump 12. During the period matching the pressure, the detection error of the fuel pressure sensor 32 may be calculated a plurality of times, and the average value thereof may be used as the detection error learning value.

  Further, in this embodiment, it is possible to estimate that the deviation δ1 (= target discharge pressure−high pressure side fuel pressure) between the target discharge pressure of the low pressure pump 12 and the fuel pressure (actual fuel pressure) on the discharge side of the high pressure pump 14 has become zero. However, the detection error of the fuel pressure sensor 32 is learned when the deviation δ1 can be estimated in the region where the deviation δ1 ≠ 0. good. In this case, by detecting a deviation δ2 (= target discharge pressure−detected fuel pressure) between the target discharge pressure of the low-pressure pump 12 and the detected fuel pressure of the fuel pressure sensor 32, the detection error of the fuel pressure sensor 32 (= detected fuel pressure−actual fuel pressure = [delta] 1- [delta] 2) can be learned with high accuracy.

It is a figure which shows schematic structure of the high pressure fuel supply system in one Example of this invention. It is a block diagram of a high pressure pump. It is a time chart which shows the behavior of a flow control valve and a high-pressure pump. It is a figure which shows the detection characteristic of a fuel pressure sensor. It is a figure which shows the allowable error of a fuel pressure sensor. It is a figure which shows notionally a fuel pressure correction coefficient map. It is a flowchart explaining the flow of a process of a detection error learning correction routine. It is a figure which shows a detection error learning value map notionally. It is a time chart which illustrates the behavior of the high-pressure side fuel pressure (fuel pressure on the discharge side of the high-pressure pump) after the engine is stopped, and the behavior of the high-pressure side fuel pressure, the detected fuel pressure HP, and the corrected detected fuel pressure CHP after the engine start. (A), (b) is a time chart which illustrates the behavior of the high-pressure side fuel pressure, the engine speed, and the battery voltage when starting at temperatures of −8 ° C. and −25 ° C., respectively.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Fuel tank, 12 ... Low pressure pump, 14 ... High pressure pump, 15 ... Fuel pressure regulator (low pressure pump discharge pressure adjusting means), 18 ... Pump chamber, 19 ... Plunger, 20 ... Cam shaft, 21 ... Cam, 22 ... Flow control Valve, 23 ... Suction port, 24 ... Discharge port, 25 ... Check valve, 26 ... Valve body, 27 ... Spring, 28 ... Norenoid, 31 ... Fuel injection valve, 32 ... Fuel pressure sensor, 34 ... Pulsation damper, 36 ... ECU (learning means, detected fuel pressure correcting means, injection amount correcting means)

Claims (7)

A low pressure pump for pumping fuel in the fuel tank, a low pressure pump discharge pressure adjusting means for adjusting a discharge pressure of the low pressure pump to a target discharge pressure, and a fuel injection valve by pressurizing fuel discharged from the low pressure pump to a high pressure In an internal combustion engine comprising a high-pressure pump for pumping and a fuel pressure sensor for detecting a fuel pressure on the discharge side of the high-pressure pump,
There is a predetermined learning execution condition that the detected fuel pressure of the fuel pressure sensor is in a low fuel pressure region below a predetermined value , and when the condition is satisfied , the deviation between the target discharge pressure of the low pressure pump and the detected fuel pressure of the fuel pressure sensor Learning means for learning the detection error of the fuel pressure sensor based on
Detecting fuel pressure correcting means for correcting the detected fuel pressure of the fuel pressure sensor based on the learning value of the learning means from the low fuel pressure region after learning of the detection error of the fuel pressure sensor by the learning means is completed. A fuel pressure detecting device for an internal combustion engine characterized by the above.   The learning means learns a detection error of the fuel pressure sensor when a deviation between a target discharge pressure of the low pressure pump and a fuel pressure on the discharge side of the high pressure pump can be estimated. An internal combustion engine fuel pressure detection device according to claim 1.   The learning means learns the detection error of the fuel pressure sensor when it can be estimated that the fuel pressure on the discharge side of the high pressure pump has increased to the target discharge pressure of the low pressure pump after the low pressure pump is started. The internal combustion engine fuel pressure detection device according to claim 2.   The learning means learns a detection error of the fuel pressure sensor when a predetermined time required for the fuel pressure on the discharge side of the high pressure pump to rise to the target discharge pressure of the low pressure pump elapses after the low pressure pump is started. The fuel pressure detection device for an internal combustion engine according to claim 3, wherein   The fuel pressure detection device for an internal combustion engine according to claim 1 or 2, wherein the learning means learns a detection error of the fuel pressure sensor for each region of a specific operating parameter that affects the fuel pressure. Temperature detecting means for detecting the fuel temperature or any temperature correlated therewith,
6. The fuel pressure detection apparatus for an internal combustion engine according to claim 5, wherein the learning means learns a detection error of the fuel pressure sensor for each temperature region detected by the temperature detection means.   The learning means does not learn the detection error of the fuel pressure sensor when the low-pressure pump is started in a state where the stop time of the internal combustion engine is short and the residual fuel pressure on the discharge side of the high-pressure pump does not completely escape. The fuel pressure detection device for an internal combustion engine according to any one of claims 1 to 6.

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